The invention relates to the interconnection and packaging of electronic components and, more particularly, to a circuit module such as an RF transponder for monitoring a condition within a pneumatic tire.
As used herein, the term xe2x80x9ccircuit modulexe2x80x9d refers to an interconnection substrate such as a printed circuit board (PCB) having electronic components mounted thereto. A PCB is a multi-layer substrate, having alternate layers of insulating material and conductive material. The conductive material is patterned to have conductive xe2x80x9clinesxe2x80x9d or xe2x80x9ctracesxe2x80x9d for routing signals (and power) from one location on the PCB to another location on the PCB. Electronic components are interconnected with one another by the conductive traces. Conductive traces may be disposed on both sides (surfaces) of the PCB. Examples of electronic components which may be incorporated in a circuit module include:
(a) xe2x80x9cactivexe2x80x9d electronic components such as integrated circuit (IC) devices, and the like;
(b) xe2x80x9cpassivexe2x80x9d electronic components such as resistors, capacitors, and inductors (including transformers), and the like;
(c) switches, relays and the like; and
(d) sensors, transducers and the like.
In some cases, a circuit module is intended to be disposed in a xe2x80x9charshxe2x80x9d environment, and it is desirable to isolate the electronic components of the circuit module from such an environment. An example of such an application for a circuit module is an RF transponder which is disposed within a pneumatic tire of a vehicle. In such applications, it is generally desirable to encapsulate or otherwise package the circuit module to isolate the electronic components from the environment.
As used herein, a xe2x80x9ctransponderxe2x80x9d is an electronic apparatus (device) capable of monitoring a condition such as air pressure within a pneumatic tire, and transmitting information (a signal) indicative of the monitored condition to an external device. The external device can be either an RF (radio frequency) reader/interrogator or, simply an RF receiver. A simple receiver can be used when the transponder is xe2x80x9cactivexe2x80x9d, and has its own power source. A reader/interrogator would typically be used when the transponder is xe2x80x9cpassivexe2x80x9d and is powered by an RF signal from the reader/interrogator. In either case, in conjunction with the external device, the transponder forms a component of an overall tire-condition monitoring/warning system.
In order to send and receive RF signals, a transponder must have an antenna. The antenna may either be incorporated into the transponder module itself, or it may be external to the transponder module and electrically connected or coupled to it in a suitable manner.
U.S. Pat. No. 4,724,427 (Carroll; 1988), incorporated in its entirety by reference herein, discloses a transponder device. FIG. 9 of the patent, shows a topographical representation of a transponder chip (100) in an embodiment that includes an antenna coil (104) as part of a monolithic chip (102). As disclosed therein, the coil (104) is etched around the periphery of the monolithic chip also known as the chip substrate (102). In the center of the coil (104) are found a custom logic circuit (106), a programmable memory array (108), and a memory control logic (110). Using the chip topography shown in this figure, a functionally complete transponder may be realized on a single semiconductor chip. (see column 11, lines 7-22; numbers edited)
In a similar manner, U.S. Pat. No. 5,345,231 (September 1994) discloses a contactless inductive data-transmission system. FIG. 7 of this patent shows components of a chip having a substrate (52) which can be photolithographically deposited along with antenna coils (50) which can be in a plane above the semiconductor topography (51) of the chip. (column 7, lines 14-17) In both this patent and the aforementioned U.S. Pat. No. 4,724,427, the antenna coils are disposed around the periphery of the IC chip, surrounding the components and periphery of the IC chip.
U.S. Pat. No. 5,574,470 (de Vall; 1996), incorporated in its entirety by reference herein, discloses a radio frequency identification transponder apparatus and method. A transponder is formed of a very thin flexible dielectric substrate (10) on opposite sides of which are formed first (26) and second (31) series-connected halves of a single antenna coil having ends connected to an integrated circuit die (50) mounted to a die bond site (46) at a corner of the substrate (10). Conductive vias (22,24) extend through the substrate (10) to effect connection between the antenna halves (26,31), from one side of the substrate to the other side of the substrate. Protective laminates (58,60) on either side of the substrate (10) are bonded to one another around the substrate edges, and also are bonded to one another at interior portions through a slot (20) formed in the substrate (10).
The following patents, all of which are incorporated in their entirety by reference herein, are cited as being of interest: 5,923,300; 5,894,006; 5,879,502; 5,870,066; 5,854,480; 5,461,545; 5,420,757; 5,345,231; 5,313,365; 5,250,843; 5,223,851; 5,218,861; 5,214,410; 5,181,975; 4,911,217; 4,851,855; 4,795,693; 4,724,427; 4,628,148; 4,524,324; and 4,092,487.
According to the invention, a circuit module comprises a first printed circuit board (PCB) having a first surface and a second surface, electronic components mounted to its first surface, a first long conductive spiral trace on its first surface and a second long conductive spiral trace on its second surface, wherein the second long conductive trace is connected in series with the first long conductive trace to form a coil which is connected to the electronic components.
In a second embodiment, other PCBs are stacked parallel to the first PCB, each having a first surface and a second surface, and each having a long spiral conductive trace on its first surface and/or on its second surface. Still other PCBs having no traces may be stacked between the PCBs having traces in order to separate a long trace of one PCB from a long trace of another PCB. A PCB adjacent to, but not possessing, the electronic components may be in the form of a ring having an opening, wherein the opening forms a cavity for containing the electronic components. The long conductive traces are attached all in series with each other to form a single air core antenna coil, and the circuit module functions as a RF transponder.
In a third embodiment, the long conductive traces can be attached in two separate series to form two windings of a coupling transformer, in which one winding (comprised of one or more traces connected in series) is connected to the electronic components, and the other winding (also comprised of one or more traces connected in series) is connected to an external antenna. The external antenna can be a coil of wire disposed circumferentially (360-degrees) around an inner surface of a pneumatic tire, and the circuit module functions as a RF transponder.
In a variation of the second embodiment, a ferrite antenna comprising a coil of wire wound about a ferrite rod is disposed within the cavity formed by the opening in one of the PCBs. The ferrite antenna is aligned parallel with the PCBs, and thus perpendicular with respect to the axis of the coil formed by the long traces, to provide a dual-polarized antenna system.
In a variation of any of the embodiments, the long spiral conductive traces of some or all of the PCBs can be attached to each other in parallel, to improve performance by way of reduced electrical resistance if the spiral coils are made of very fine pitched traces.
Any of the above embodiments of an RF transponder circuit module can be encapsulated within molding material disposed on all external surfaces of the circuit module. The molding material can be any rubber, ethylene propylene diene monomer (EPDM) rubber, butyl rubber, natural rubber, neoprene and mixtures thereof, a mixture of chlorobutyl rubber and natural rubber, or a mixture of styrene-butadiene rubber (SBR) and natural rubber.
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.